There are herbs that help put on the weight, but you want to put on muscle and not just weight. Over weight people do not like seeing a person loose weight and complain the most.
I would rathure see tight muscles my self. The strongest man in the world about 25 years ago had zero fat and almost zero strong looking muscles. His bones all shown and the muscles he did have were super tight to the bone. He picked up 1,400# above his head like it was nothing. The muscle bound body builders may have huge muscles, but they may not be as strong as one thinks and their health is against nature or should I say not natural and Nature always wins.